1. Field of the Invention
The present invention relates to speed reducers adapted to ensure angular actuation of the movable mobile members of robots, industrial manipulators, rotary machining plates and other like applications.
2. History of the Related Art
It is known that, in this type of apparatus, there is provided for each movable member a kinematic chain comprising an input shaft driven by an autonomous motor and connected, via a speed reducer, to an output shaft secured to the member in question. As the speed of rotation of the input shaft is much higher than that desired for the output shaft, reducers of the cycloidal type are ordinarily employed.
It will be recalled that a conventional cycloidal reducer comprises in principle at least one eccentric (in fact, two opposite eccentrics are most often employed in order to obtain a better balancing of forces), which is connected to the input shaft to ensure, by rotation, the control of a circular cam whose periphery is toothed in order to cooperate with a fixed toothing. The number of teeth of this fixed toothing is very slightly greater (in practice by one unit) than that of the periphery of the cam. With the cam are associated, in addition, actuation fingers which are carried by a plate angularly connected to the output shaft and which are engaged inside housings made in the cam (or, in the ordinary case of two parallel cams, in a housing defined by two conjugate openings of the two cams).
It will be understood that the primary motion applied by the input shaft to the eccentric causes the corresponding toothed cam to roll on the fixed outer toothing and thus to ensure, via the actuation fingers, drive of the output shaft in a ratio which depends on the number of teeth of the cam and on the difference of this number with respect to that of the fixed toothing, the cam backing by this difference for a revolution of the eccentric.
FIG. 1 of the accompanying drawings schematically shows the structure generally adopted for a cycloidal reducer with two eccentrics.
The fixed frame of the reducer in question is constituted by the assembly of two parts 1 and 2 of annular profile. This frame 1-2 supports an input shaft 3 which is driven in rotation by a motor shown schematically at 4 and on which is fitted a pinion gear 5. The latter meshes with the inner toothing 6a of a ring 6, disposed coaxially about frame 1-2 while being supported by two bearings 7 and 8 respectively mounted, the first, in a fixed cover 9 secured to the frame 1-2, the second, in a rotary plate 10. This plate 10 is carried by the frame 1-2 with the aid of a roller bearing 11 and it is provided, opposite the fixed plate 9, with an annular flange 10a forming an output shaft for the reducer.
The outer wall of ring 6 is machined in order to present two eccentric annular bearing surfaces 6b and 6c, the eccentricities being disposed opposite one another. On each of these bearing surfaces is mounted, with the interposition of a roller bearing 12, a cam 13 or 14, respectively, which is made with an annular profile and whose periphery is provided to be toothed so as to cooperate with the inner toothing of a fixed ring gear 15. The toothing 15a of the fixed ring gear 15 comprises a number of teeth very slightly greater (in fact by one or two units) than that of the toothings 13a and 14a of the cams 13 and 14, the cam being, to that end, made with a primitive diameter slightly smaller than the primitive diameter of the inner wall of the ring gear 15.
In order to ensure suitable guiding of the rotary plate 10 on the fixed parts of the assembly, the outer edge of the plate projects with respect to the ring gear 15 secured to the cover 9 and it receives a roller bearing 16 maintained in place with the aid of an annular cover 17.
Each of the toothed cams 13 and 14 is provided with a series of circular openings 13b, 14b. Once the openings of the two cams are brought into register with respect to one another, there is introduced in each of the housings thus defined an actuation finger constituted, in the conventional construction illustrated in FIG. 1, by a bushing 18 mounted idly, with a clearance as reduced as possible, on a cylindrical support or pin 19, which is carried by the plate 10.
Correct functioning of such a system implies employing parts which require a precise machining, followed by a very thorough grinding. Furthermore, it is virtually impossible for the torque to be simultaneously transmitted by a plurality of fingers 18-19, which leads to increasing the dimensions of the device.
It is an object of the present invention to overcome these drawbacks and to simplify the construction of the cycloidal reducers of the type shown, reduce the dimensions thereof and to improve the functioning thereof.